New data suggests the chances of developing flu are cut by doing two and a half hours of vigorous exercise each week.

The London School of Hygiene and Tropical Medicine's online Flu Survey received around 4,800 answers.

Now in its fifth year, the Flu Survey attempts to record as much detail as possible about who does and doesn't catch the illness.

One of the questions people are asked is how many hours vigorous exercise they do a week, which includes running, fast cycling and competitive sports ranging from none to five hours. They are also asked whether they are around children, if they have been vaccinated and their age. Respondents are then asked to log in each week and note how they feel and whether they have any flu-like symptoms.

The researchers found that 100 cases of flu per 1,000 people could be avoided by engaging in vigorous exercise, but said moderate exercise did not appear to have a protective effect.

Overall this year's survey found some of the lowest numbers of flu cases in recent years, with only 4.7% of reports telling of positive flu-like symptoms compared to six per cent last year.

Children also appear to have had lower levels of illness than last year, with only 5% reporting symptoms compared with 7.9% the year before.

The London School of Hygiene and Tropical Medicine's Dr Alma Adler said, "We need to treat this result cautiously as these are preliminary findings. However, they are consistent with findings for other conditions and really show the health benefits of exercise. Although many people have dodged the flu bullet this winter, flu can occur at any time, so taking advantage of the better weather give us a great opportunity to get out and get fit to ward off flu this spring."